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Difficulty: MediumRelief and Major Landforms of Africa

Arrange the following stages in the structural evolution and landform development of the East African Rift System in order from the initial tectonic stage to the final landform stage.

  1. 1Regional crustal doming and thermal upwarping of the continental lithosphere
  2. 2Development of parallel tensional normal faults across the stretched dome
  3. 3Subsidence of the central rift floor (graben) between opposing escarpments
  4. 4Extrusive volcanism along active fracture zones generating massive volcanic cones

Answer

The correct sequence from initial tectonic activity to final landform formation is: Regional crustal doming and thermal upwarping of the continental lithosphere → Development of parallel tensional normal faults across the stretched dome → Subsidence of the central rift floor (graben) between opposing escarpments → Extrusive volcanism along active fracture zones generating massive volcanic cones.
The East African Rift Valley system evolved chronologically starting with mantle upwelling that caused broad crustal doming. Continued extensional stress produced parallel normal faults. The block between these faults subsided to form a graben (rift floor), and subsequent magmatic activity along these fault fissures constructed isolated volcanic peaks like Mount Kilimanjaro.

Step-by-Step Solution

1
Identify the primary sub-crustal driver initiating rifting in East Africa.
Mantle plume activity leads to thermal expansion and regional lithospheric doming.
Before continental crust can rift, mantle heat causes upwarping and stretching of the overriding plate.
2
Determine the mechanical response of the stretched crust to ongoing tension.
Parallel normal faults form across the axis of the uplifted dome.
Tensional forces exceed the tensile strength of the brittle upper crust, creating deep parallel fracture lines.
3
Analyze the formation of the rift valley's characteristic depression and rim relief.
The central block sinks down relative to the fault walls, creating a graben flanked by steep horst escarpments.
Down-faulting of the central block creates the classic linear trough of the East African Rift Valley.
4
Identify the late-stage volcanic landform features associated with mature rifting.
Magma rises along fault conduits to build massive volcanic cones on the rift floor and shoulders.
Deep-seated fractures provide pathways for mantle melt to reach the surface, producing volcanic structures like Mount Kilimanjaro and Mount Kenya.

Key Concept

Tectonic evolution and sequential landform genesis of the East African Rift Valley system
Estimated Time:1m 15s
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Topics

Relief and Major Landforms of Africa

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